Does Tartan=Plaid?

For those who don't know me, I'm a huge fan of plaid. There's just something warm, inviting and, of course, traditional about the colors and linear patterns of his timeless fabric and design. In the past, I've often used the words 'plaid' and 'tartan' interchangeably, assuming that they were more or less one and the same. Several months ago I accompanied an interior design client to a house in which she was doing work on and which I was commissioned to do a live edge cocktail table for. She described the pillows that were to go on a sofa that was being custom built as tartan. I told her how much I loved plaid, and she proceeded to tell me that she thought of using various plaid patterns she decided on straightforward tartan - well, I kinda looked at her funny but decided to keep my mouth shut, taking in confusion on my part. Isn't plaid and tartan the same?

Fast forward to an article today in the LA Times on with my hero Scot Meacham Woods, once and for all, explaining the difference between the two:

Discerning trendsters take note: Wood points out that while all tartans are plaids, not all plaids are tartans. "If you look at a plaid, it is basically stripes running in a horizontal direction and stripes running in a vertical direction; that's a plaid. If the arrangement of the stripes is exactly the same in both directions ... creating a grid pattern, that's when you get into tartan territory."